Coffee with milk, no sugar

On the wiretaps people kept ordering coffee with milk. The waiter at the club café still doesn't know whether it was meant to have sugar. Some clues in this case come as riddles. If one stumps you, a hint will solve it. Four people and one whistle: one person per row, one per column. Whoever is left alone with it in the same room is the one you're looking for.

Suspects

• Aniceto, the café waiter: He's been serving coffee with milk for forty years. Since the wiretaps, some people leave him very strange tips.
• Balbina, the president's secretary: She always answers with the same line: "the president isn't in, but you can leave a message".
• Celso, the assistant referee: At matches he runs the whole touchline. In the café he never leaves his table.
• Dulcineia, the sports reporter: She wrote about fruit for two years. She had never written so much about food.